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151.
The presence of heavy metal concentrations was examined in natural sediments from four sites along the Jajrood river in northeast
of Tehran, the capital of Iran. Besides determination of elemental concentrations (Pb, Cu, Zn, Cd, Ni and Cr), X-ray fluorescence
and X-ray diffraction tests were carried out to determine other chemical components in these adsorbents. Also the ability
of sediments to adsorb these heavy metal ions from aqueous solutions was investigated. Results show that the extent of adsorption
increases with increase in adsorbent concentration. The amount of adsorbed Pb, Cu and Zn in sediments was much greater than
that of the other metals, and Cr was adsorbed much less than others. The adsorbabilities of sediments to heavy metals increased
in the order of Pb > Cu > Zn > Cd > Ni > Cr. Based on the adsorption data, equilibrium isotherms were determined at selected
areas to characterize the adsorption process. The adsorption data followed Freundlich and Langmuir isotherms in most cases.
Correlation and cluster analysis was performed on heavy metals adsorption and sediment components at each site to evaluate
main adsorbing compounds in sediments for each metal. Results demonstrated that heavy metals sorption is mostly related to
load of organic matter in the Jajrood river sediments. 相似文献
152.
Water resources in Egypt are becoming scarce and the demand for clean drinking water supply is one of the most important priorities of the Egyptian government in recent years. Analyzing water use and future demand forecasting is a primitive clue for water demand management. Water in Luxor is used for agricultural, residential, institutional, commercial, and touristic purposes. The results of water use analysis indicated that for the time period from 1983 to 2012, agriculture is the highest consumer of water which reached about 94.76–97.38 % followed by residential water consumption (1.90–3.05 %), institutional water consumption (0.71–1.75 %), and touristic water consumption (0.02–0.43 %), respectively. The future demand forecasting results revealed that the present situation may continue to rise in the next 50 years which will increase the water demand with a water deficit ranging between 15 and 114 MCM/year. To fill the gap between the present water consumption and future residential, institutional, commercial, and touristic water demand, additional municipal facilities, and improvement and management of water supply/demand are needed. To cope with the predicted future water demand, it is recommended to improve the on-farm irrigation, reduce the demand for irrigation water, rationalize the irrigation water use, and enhance the integrated role of water users in integrated water resources management. 相似文献
153.
Back analysis of an excavated slope failure in highly fractured rock mass: the case study of Kargar slope failure (Iran) 总被引:2,自引:1,他引:1
Mostafa Sharifzadeh Mohsen Sharifi S. Mohammad Delbari 《Environmental Earth Sciences》2010,60(1):183-192
This paper examines the failure of Kargar cut slope located at the south part of Esfahan subway using analytical and numerical
back analysis methods. The excavated trench has 27 m depth with near vertical walls due to the space limitation around it.
The geology of the area comprises weathered and heavily jointed shale and sandstone overlaid by alluvium deposits. Despite
the slope being supported by shotcrete and fully grouted rock bolts, a catastrophic failure occurred at the east wall. Due
to the uncertainty about the causes of failure initiation, back analyses have been performed via both the limit equilibrium
and numerical method for considering various probable mechanisms. In the back analysis with limit equilibrium method, the
rock mass is assumed as an equivalent continuum and Hoek–Brown failure criterion and geological strength index (GSI) are applied
to calculate the shear strength parameters. The results show that GSI value was 33 in the failed mass. In the numerical back
analysis, the distinct element method is applied to study the contribution of rock joints to the failure and progressive rock
mass strength degradation until failure. The results show that threshold values of joint cohesion and friction were 0.2 MPa
and 30°, respectively. Also the modeled slip surface being step-shaped agrees with the observed one. 相似文献
154.
We study thermal instability in a magnetized and partially ionized plasma with charged dust particles. Our linear analysis shows that the growth rate of the unstable modes in the presence of dust particles strongly depends on the ratio of the cooling rate and the modified dust-cyclotron frequency. If the cooling rate is less than the modified dust-cyclotron frequency, then the growth rate of the condensation modes does not modify due to the existence of the charged dust particles. But, when the cooling rate is greater than (or comparable to) the modified dust-cyclotron frequency, the growth rate of unstable modes increases because of the dust particles. Also, the wavenumber of the perturbations corresponding to the maximum growth rate shifts to the smaller values (larger wavelengths) as the cooling rate becomes larger than the modified dust-cyclotron frequency. We show that the growth rate of the condensation modes increases with the electrical charge of the dust particles. 相似文献
155.
Mohsen Jalali 《Environmental Geology》2009,57(5):1011-1020
In areas of intensive crop production, continual phosphorous (P) applications as P fertilizer and farmyard manure have been
made at levels exceeding crop requirement. As a result, surface soil accumulations of P have occurred to such an extent that
loss of P in surface runoff and a high risk for P transfer into groundwater in concentrations exceeding the groundwater quality
standard has become a priority management concern. Phosphorous content of groundwater was determined in order to examine dissolved
P concentration and species in the groundwater and mineral solubilitiy in a semi-arid region of southern Malayer, western
Iran. The speciation for P in groundwater was calculated using geochemical speciation model PHREEQC. The concentration of
total P in the groundwater (0.01–2.56 mg P l−1) and estimated concentrations of HPO4
2− (49.5–89%), H2PO4
− (1.5–17.3%), CaHPO4
+ (5.7–36.1%), and CaPO4
− (1.4–12.2%) varied considerably amongst the groundwater. Results suggest that the concentration of P in the groundwater could
be primarily controlled by the solubility of octacalcium phosphate and β-tricalcium phosphate. Large amounts of P fertilizer,
inadequate management of P fertilization, and low irrigation efficiency, coupled with sandy soils in some parts of the study
area could be mainly responsible for the greater P in the groundwater. In general, the greater the dissolved P concentration
in the groundwater, the closer the solution was to equilibrium with respect to the more soluble Ca-phosphate minerals. The
groundwater P content could be potentially used to identify areas where management approaches, such as P applied and crop
type planted, could be adjusted to different types of soils, geology and topography. 相似文献
156.
Federico Rossetti Mohsen Nasrabady Gianluca Vignaroli Thomas Theye Axel Gerdes Mohammad Hossein Razavi Hosein Moin Vaziri 《地学学报》2010,22(1):26-34
The ophiolitic mélange of the Sabzevar Range (northern Iran) is a remnant of the Mesozoic oceanic basins on the northern margin of the Neotethys that were consumed during the Arabia–Eurasia convergence history. Occurrence of km-scale, dismembered mafic HP granulitic slices is reported in this study. Granulites record an episode of amphibole-dehydratation melting and felsic (tonalite/throndhjemite) melt segregation at c. 1.1 GPa and 800 °C. In situ U(-Th)–Pb geochronology of zircon and titanite grains hosted in melt segregations points to an Early Cretaceous (Albian) age for the metamorphic climax. Results of this study (i) impose reconsideration of the current palaeotectonic models of the Neothetyan convergent margin during the Early Cretaceous and (ii) argue that punctuated events of subduction of short-lived back-arc oceanic basins accompanied the long-lasting history of the Neotethyan subduction in the region. 相似文献
157.
Mohammad Khandan Bakavoli Ebrahim Haghshenas Mohsen Kamalian 《Soil Dynamics and Earthquake Engineering》2011,31(5-6):737-756
Two hilly sites were selected to study seismic site response due to topography effects. The sites were selected in a manner to be as much as possible homogenous and free of the soft soil layers effects. The hills were instrumented by nine velocimetric stations to record microtremors and the obtained data were analyzed using horizontal to vertical spectral ratios. Some standard spectral ratio tests were performed on noise as well. Then the instrumented hills were modeled (both 2D and 3D) assuming a linear elastic constitutive behavior subjected to vertically propagating SV and P Ricker wavelets. All calculations were performed in time domain using direct boundary element method. Different transfer function components, amplification patterns and spectral ratios were calculated in frequency domain. The frequency of vibration, obtained by experimental studies, is between 4 and 5 Hz for both of the hills. The spectral ratios derived by numerical simulations were compared with the observed spectral ratios. They show relatively good similarities between the results of these two methods. The frequencies of vibration derived from different methods seem to be nearly identical. The agreement in term of resonance frequency between microtremors and numerical modeling suggests that noise measurements could represent a simple, even if preliminary, tool in order to identify possible topographic amplification. 相似文献
158.
Albian oceanic anoxic events in northern Tunisia: Biostratigraphic and geochemical insights 总被引:1,自引:0,他引:1
Albian pelagic successions of the Nebeur area in northwestern Tunisia consist of radiolarian-bearing and organic-rich black shale beds, which represent the lower part of the Fahdene Formation. The carbonate content of the organic-rich beds ranges between 40 and 48%. Total organic carbon (TOC) analyses via Rock Eval pyrolysis yielded values ranging between 0.7 and 2.8% and a mixed marine/terrestrial origin. Tmax values vary between 424 and 450 °C, indicative of submature to mature organic matter. High resolution planktic foraminiferal and radiolarian biostratigraphy suggest that the black shales beds span the mid- to late Albian, confined to the middle part of the Ticinella primula zone, upper Biticinella breggiensis zone and lower appeninica + buxtorfi zone. Episodes of organic-rich deposition in the “Tunisian Trough” are interpreted as being the sedimentary record of the global oceanic anoxic events OAE1b, c, and d respectively. Age-diagnostic radiolarian assemblages recovered from late Albian organic-rich black shales lie within the UA13–UA14 boundary biochronozones. The abundance of radiolarian and calcispheres (i.e. pithonella) within the black shales suggests high productivity periods and eutrophic conditions probably triggered by upwelling currents. 相似文献
159.
Effects of non-rigid muddy bed on the wave climate at the Hendijan coast along the northwestern part of the Persian Gulf have been examined through field measurements and numerical wave transformation modeling. The field survey included measurements of wave characteristics at an offshore and a nearshore station, and mud sampling to obtain the thickness of the fluid mud layer and its rheological properties. Comparisons of wave spectra at the two stations show energy dissipation along the wave trajectory with higher dissipation in the wave period band around 6?s, because depending on the site a given frequency band tends to be more effective in wave–mud interaction. Dissipation induced by the non-rigid bed is introduced into the REF/DIF wave transformation model through the application of viscoelastic constitutive equations for fluid mud. Numerical outputs of the nearshore wave height, for which the viscoelastic parameters included in the model were obtained independently from oscillatory frequency-sweep tests, are found to be comparable with measured values at the nearshore station. This implies that the model is useful for estimating the design wave conditions in the study area. 相似文献
160.
The objective of this paper is to investigate the rheological behavior of kaolinite and Hendijan mud, located at the northwest part of the Persian Gulf, and the dissipative role of this muddy bed on surface water waves. A series of laboratory rheological tests was conducted to investigate the rheological response of mud to rotary and cyclic shear rates. While a viscoplastic Bingham model can successfully be applied for continuous controlled shear-stress tests, the rheology of fluid mud displays complex viscoelastic behavior in time-periodic motion. The comparisons of the behavior of natural Hendijan mud with commercial kaolinite show rheological similarities. A large number of laboratory wave-flume experiments were carried out with a focus on the dissipative role of the fluid mud. Assuming four rheological models of viscous, Kelvin-Voigt viscoelastic, Bingham viscoplastic, and viscoelastic-plastic for fluid mud layer, a numerical multi-layered model was applied to analyze the effects of different parameters of surface wave and muddy bed on wave attenuation. The predicted results based on different rheological models generally agree with the obtained wave-flume data implying that the adopted rheological model does not play an important role in the accuracy of prediction. 相似文献